Bath for the electroless deposition of ductile copper

ABSTRACT

IN WHICH R1 IS AN ALIPHATIC OR CYCLIC GROUP AND R2 IS H, A SULPHATE GROUP, A PHOSPHATE GROUP OR AN ACID CHLORIDE THEREOF, (A+B+C) HAS A VALUE OF BETWEEN 20 AND 500 AND THE THIOETHER OF POLYALKYLENE GLYCOL IS PERCENT IN A QUANTITY OF BETWEEN 0.001 AND 0.5% BY WEIGHT.   R1-S(C2H4O)A(C3H6O)B(C2H4O)C-R2,   1. AN ALKALINE AQUEOUS COPPER-PLATING BATH FOR THE DEPOSITION OF DUCTILE COPPER COMPRISING AS ESSENTIAL CONSTITUENTS: 0.01-0.15 MOL OF A COPPER SALT SOLUBLE IN WATER, 0.01-0.80 MOL OF A COMPOUND FORMING COMPLEXES WITH CUPRIC IONS, 0.01-0.35 MOL OF FORMALDEHYDE OR A COMPOUND PRODUCING FORMALEDHYDE, 0.05-0.50 MOL OF ALKALI HYDROXIDE (PH$11-13.5),AND A THIOETHER OF A POLYALKYLENE GLYCOL, CHARACTERIZED IN THAT THE THIOETHER IS DEFINED BY THE FOLLOWING FORMULA:

United States Patent 3,843,373 BATH FOR THE ELECTROLESS DEPOSITION 0F DUCTILE COPPER Arian Molenaar, Jan Boven, and Johannes Engelbertus Adrianus Maria van den Meerakker, Emmasingel, Eindhoven, Netherlands, assignors to US. Philips Corporation, New York, N.Y.

No Drawing. Filed Sept. 26, 1973, Ser. No. 400,880 Claims priority, application Netherlands, Oct. 5, 1972, 7213464 Int. Cl. C23c 3/02 US. Cl. 1061 2 Claims ABSTRACT OF THE DISCLOSURE An alkaline aqueous copper-plating bath comprising 0.01-0.15 mol copper salt,

0.010.80 mol oomplexing agent for cupric ions,

0.010.35 mol formaldehyde,

0.05-0.50 mol alkali hydroxide (pH 11-135) and between 0.001 and 0.5% by weight of the compound in which R is an aliphatic or cyclic group and R is hydrogen, sulphate, phosphate or an acid chloride thereof, while 20 a+b+c 500.

The invention relates to an alkaline aqueous bath for the electroless deposition of ductile copper and provides methods of operating such a bath.

In this connection electroless copper plating is understood to mean the deposition by means of chemical re duction of an adherent copper layer on a susceptible surface in the absence of an external source of electricity. Such a copper-plating operation is performed, for example, on a large scale for the manufacture of printed wiring boards, conducting coatings which are subsequently further coated electrically, and for decorative purposes.

Such an aqueous alkaline copper-plating bath is described in UK. patent appl. 48,590/ 70, US. patent appl. Ser. No. 78,740, filed Oct. 7, 1970, and now abandoned, which bath comprises as essential constituents: 0.010.15 mol of a copper salt soluble in water, a total of 0.01-0.80 mol of one or more complexing agents preventing cupric ions from being deposited from the alkaline solution, 0.05-0.50 mol of alkali hydroxide (pH approximately 11-135), 0.01-0.35 mol formaldehyde or a compound producing formaldehyde and for improving the ductility of the depositing copper an effective concentration of a soluble non-ionic or ionic polyalkylene oxidic compound constituting or not constituting micelles and comprising at least 4 alkylene oxide groups.

The known compounds may be used as eomplexing agents such as, inter alia, potassium sodium tartrate, triethanol amine, ethylene diamine tetra-acetic acid, diethylene triamine penta-acetic acid, cyclohexane diamine tetra-acetic acid, nitrilo-triacetic acid or N-hydroethyl ethylene diamine triacetic acid.

An effective concentration of the polyalkylene oxidic compound is understood to mean a concentration giving an improvement of the ductility and-if insuflicient ductile copper is deposited from the solution without the active compound-is at least so large that a ductility of at least 2 bends is obtained. An effective concentration also substantially always gives an improvement of the colour and the smoothness of the deposition and frequently a reduced blister formation in the surface of the deposited copper and an improved adhesion of the deposited coating.

According to a preferred embodiment of the copperplating bath described in this patent application this bath contains polyalkylene oxidic compounds of the type thio- 3,843,373 Patented Oct. 22, 1974 ether of an alkyl mercaptane and polyethylene glycol defined by the formula:

According to US. patent specification 3,361,580 bivalent sulphur compounds added in a quantity which is smaller than that completely obviating the copper deposition have a stabilizing effect on. a bath for electroless copper plating. The limits of the active quantity which must be present lie between 10' and 10*% by weight and preferably between 10" and 2 l0- by weight. US. patent specification 3,222,195 recommends Z-mercaptobenzothiazol as a stabilizer, while US. patent specification 3,392,035 employs a stabilizer having the structure CH (CH SH in which (n=715 for the deposition of thin copper layers.

Copper-plating baths of the three latter types of bivalent sulphur compounds generally yield brittle and dark coloured copper deposits. In addition these sulphur compounds can only be used in low concentrations because otherwise the copper deposition is completely discontinued owing to poisoning of the bath.

Copper deposition is not effected in a copper-plating solution having a temperature of 50 C. and comprising 0.03 mol of a copper salt soluble in water, 0.031 mol of a compound forming complexes with cupric ions, 0.10 mol of formaldehyde or a compound producing formaldehyde and 0.15 mol of alkali hydroxide to which 3 10 by weight of thiourea, phenylmercaptotetrazol, sodium thiosulphate or butyl mercaptane is added.

According to the previously mentioned UK. patent application 48,590/70, US. patent application Ser. No. 78,740 in the name of the applicant, thioethers with a higher alkyl group and polyethylene glycol are added in higher concentrations without the copper deposition be ing discontinued while the quality of the deposited copper as regards ductility is improved. The compounds mentioned in the description of this application are commercially available surface-active materials which comprise less than 10 to 20 ethylene oxide groups.

The compounds of this type hitherto used were found to be not quite satisfactory notably with respect to the bath stability and the ductility of the copper layer in case of increased rates of depositions.

In fact it was found during the investigation which led to the invention that the molecule of the said thioethers consists of a part to which a stabilizing action may be ascribed and a part to which a regulating action, i.e., an action regulating the deposition rate is to be ascribed.

These groups are to be chosen carefully so as to yield a bath having an optimum action in the combined addition.

The said investigation also showed that it is essential that the groups are combined to one molecule. When the two components occur in separate compounds this is considerably less effective.

The bath according to the invention which in addition to the above-mentioned components comprises a thioether of a polyalkylene glycol is characterized in that the thioether is defined by the following formula:

1" 2 4 )a.( 3 6 )b( 2 4 )c- 2 in which R is an aliphatic or cyclic group and R is H, a sulphate group, a phosphate group or an acid chloride thereof, (a+b+c) has a value of between 20 and 500 and in which the thioether of the polyalkylene glycol is present in a quantity of between 0.001 and 0.5 by weight.

The invention will be illustrated by the following examples.

EXAMPLE 1 Glass plates unilaterally roughened with carborundum and having a surface of 6 sq. cm. were activated for the electrodes copper deposition by moving them at room temperature for 2 min. in a solution of 50 g. stamous chloride and ml. concentrated HCl solution in 1 litre of deionized water, keeping them for l min. in running deionized water, moving them for 1 min. in a solution of 0.25 g. PdCl and 10 ml. concentrated HCl solution in 1 litre of deionized water and finally again for 1 min. in running deionized water.

Subsequently the plates were treated for 45 seconds at 75 C. with an aqueous solution comprising per litre 0.10 mol NaOH and 0.10 mol formaldehyde and Were subsequently rinsed for 5 seconds in deionized water of 75 C. They were then electroless intensified at 75 C. in 200 ml. of one of the copper-plating solutions comprising the following bath constituents per litre:

0.06 mol CuSO -5H O 0.066 mol tetra Na salt of ethylene diamine tetra-acetic acid 0.10 mol NaOH 0.10 mol formaldehyde to which one of the polyethylene glycols defined by the formula R S(C H O) H identified in the table had been added.

These compounds as well the additions in the following examples are prepared in accordance with the method as described in US. patent specification 2,588,771. Table I states the results: it proves that ductile copper is obtained at relatively high deposition rates and that the bath has a satisfactory stability. If no thioether compound is added to the copper-plating solution, copper deposition is effected within 30 min. through the entire solution. At a=-16 the deposition of the relevant copper-plating bath is discontinued after some time and the quality of the copper obtained is unsatisfactory.

TABLE I The ductility is determined by removing the copper layer partly from the substrate, bending it over 180, folding it, bending it back and flattening the fold under pressure. This series of operation is repeated until the layer breaks.

EXAMPLE 2 Glass plates similar as those in Example 1 activated and treated in the same manner were copper-plated at 75 C. in one of the following copper-plating baths having the following bath composition per litre:

0.06 mol CuCO -5HO 0.066 mol tetra Na-salt of ethylene diamine tetra-acetic acid 0.10 mol NaOH and 0.10 mol formaldehyde to which x percent by weight of polyalkylene glycol C12H 5S(C2H 0) (C3H3O)b(C2H4O) H Of the identities described in Table II had been added. The table states the results.

Glass plates of the same dimensions as those in Example l activated and treated in the same manner were copper-plated in one of the following three aqueous copperplating solutions heated at 75 C. and comprising per litre:

0.06 mol CuSO -5H O 0.066 mol tetra Na-salt of ethylene diamine tetra-acetic acid 0.10 mol NaOH 0.10 mol formaldehyde and one of the following additions:

(a) 0.03% by weight of (b) 0.03% by weight of 0:0 liv H20 (ii-S-(CzHflho-asH.

(c) 0.004% by weight of After an intensification period of three hours layer thicknesses f0 12, 15 and 16 ,am. and ductilities of 4%., 2 and 3 /2 bends, respectively, were obtained.

When 0.003% by weight of were added to the same basic solution used at C., a 15 am. thick copper layer with a ductility of 3 /2 bends had been deposited after 2 hours of intensification. The basic bath without addition of a polyoxyalkylene compound is unstable within 5 minutes.

EXAMPLE 4 Glass plates were activated and copper-plated in the manner described in Example 1 in the aqueous bath heated at 75 C. and comprising the following composition per litre:

0.06 mol CuSO -5H O 0.066 mol tetra Na salt of ethylene diamine tetra-acetic.

acid

0.10 mol NaOH 0.10 mol formaldehyde Weight Of 0121-1258 (c2H4O)7 5POC1 After an intensification of 3 hours the layer thickness of the deposited copper was 16 ,um. and its dluetjlitiy was 4 bends.

5 EXAMPLE 5 Glass plates activated in the manner as described in Example 1 were copper-plated in an aqueous solution of the following composition per litre (temperature 75 C.).

0.06 mol CuSO' -5H O 0.02 mol cyclohexane-1,2-diamine tetra-acetic acid 0.05 mol tetra Na-salt of ethylene diamine tetra-acetic acid approximately 0.20 mol NaOH to pH=12.8

f C12NH25S(C2H40)'10 86H- After 2 hours 14 m. of copper with a ductility of 3 bends had been deposited. The solution was completely stable. In the absence of the thioether of a polyalkylene glycol in the copper-plating bath this bath was unstable and was only capable of depositing brittle copper on a nuclei image.

EXAMPLE 6 Glass plates were activated in the manner described in Example 1 and subsequently treated for 47 seconds at 40 C. with a solution comprising 0.10 mol Na0H+0.10 mol formaldehyde per litre. After rinsing at 40 C. a pre-intensification was carried out for 1 /2 min. with an aqueous solution heated at 40 C. and comprising per litre:

mol CUSO4'SH20 0.031 mol tetra Na-salt of ethylene diamine tetra-acetic acid 0.10 mol NaOH 0.10 mol formaldehyde The copper image preintensified in this manner was further intensified for 3 hours in an aqueous solution heated at 40 C. and comprising per litre:

0.03 mol CuSO -5H O 0.067 mol triethanolamine 0.20 mol NaOH 0.05 mol formaldehyde at the initiation of copper-plating and another 0.05 mol after 1 /2 hour The 12 pm. thick copper layer thus obtained was maintained at a temperature of C. for /1 hour. The layer withstood 5 /2 bends before breakage occurred. When the bath did not contain the said thioether of a polyalkylene glycol, the ductility after the temperature treatment was only one bend.

What is claimed is:

1. An alkaline aqueous copper-plating bath for the deposition of ductile copper comprising as essential constituents:

0.01-0.15 mol of a copper salt soluble in water,

0.01-0.80 mol of a compound forming complexes with cupric ions,

0.01-0.35 mol of formaldehyde or a compound producing formaledhyde,

0.05-0.50 mol of alkali hydroxide (pH -1113.5), and

a thioether of a polyalkylene glycol, characterized in that the thioether is defined by the following formula:

3,661,597 5/1972 Gulla 106-1 3,472,664 10/1969 Bastenbec'k et a1. 1061 LEWIS T. JACOBS, Primary Examiner US. Cl. X.R. 117-130 E 

1. AN ALKALINE AQUEOUS COPPER-PLATING BATH FOR THE DEPOSITION OF DUCTILE COPPER COMPRISING AS ESSENTIAL CONSTITUENTS: 0.01-0.15 MOL OF A COPPER SALT SOLUBLE IN WATER, 0.01-0.80 MOL OF A COMPOUND FORMING COMPLEXES WITH CUPRIC IONS, 0.01-0.35 MOL OF FORMALDEHYDE OR A COMPOUND PRODUCING FORMALEDHYDE, 0.05-0.50 MOL OF ALKALI HYDROXIDE (PH$11-13.5),AND A THIOETHER OF A POLYALKYLENE GLYCOL, CHARACTERIZED IN THAT THE THIOETHER IS DEFINED BY THE FOLLOWING FORMULA: 